Turbines are known in the art and are used for various power generation applications. Examples of various turbines are shown in U.S. Pat. Nos. 6,233,942; 5,186,602; and 4,773,818, each of which are hereby incorporated by reference in their entirety. Turbines are classified descriptively in various categories depending upon the arrangement and operation of the particular turbine. For example, turbines may be classified as either axial flow or radial flow turbines, depending upon the flow path through the turbine. The majority of turbines used in the United States are axial flow turbines. The working fluid utilized in a turbine may be water, a combustion gas, or steam; however, the operation of a turbine is based on the same principles regardless of the type of working fluid.
A conventional axial flow turbine design includes fixed stator blades, which are usually attached to interior walls, and moving rotor blades attached to a shaft extending through the turbine. Groups of rotor and stator blades are generally assembled in an alternating arrangement within the turbine, wherein each rotor and stator pair make up a stage of the turbine. The blades are designed to have specially shaped surfaces to accommodate complex flow dynamics of the working fluid as it passes the fixed stators and moving rotors. A conventional axial flow turbine operates by the velocity change of the working fluid through the series of stator and rotor blades, whereby the working fluid imparts motion to the rotors to rotate the shaft which may be connected to a generator or propulsion device. To obtain the best possible efficiency, rotor and stator blades must be manufactured and assembled with very close tolerances to minimize leakage of working fluid around the blades. Efficiency is also improved as the turbine is run at higher rotational speeds and higher operating temperatures. To meet the demands of close tolerances, high operating speeds, and high temperatures, components used in conventional axial flow turbines must be made from special materials and manufactured to exacting tolerances, which therefore makes conventional axial flow turbines quite expensive.
High operating temperatures and rotational speeds of conventional axial flow turbines also have an affect on the service life of components used to make the turbines. The high rotational speed increases stress in components and failure of a single component can damage the entire turbine if it comes in contact another component, or worse, if it breaks off. Because such a critical failure of a turbine is to be avoided, axial flow turbines require periodic overhauls during their service life to ensure that all components are sound. These overhauls are costly and constitute a significant amount of down time during which the turbine cannot be used. Axial flow turbines, which utilize steam as a working fluid, have similar speed and tolerance requirements as axial flow turbines utilizing a combustible gas as the working fluid. In addition, steam turbines require a high steam quality, usually ninety percent or better, in order to prevent damage to the turbine.
There is thus a need for an improved turbine which has a more robust structural design that is less susceptible to critical failure when a component is damaged, and which is less costly to manufacture and maintain. There is also a need for a turbine which eliminates leakage of working fluid to provide increased efficiency. There is also a need for an improved turbine which can utilize a wider range steam quality (i.e. wetter steam) utilized as a working fluid.